Collective Rotations of Ferroelectric Liquid Crystals
at the Air/Water Interface

Patrycja Nitoń, Andrzej Żywociński, Krzysztof Noworyta and Robert Hołyst

We study four different ferroelectric liquid crystals in Langmuir monolayers on water surface. Only two of them exhibit the collective rotations induced by evaporation of water through the monolayer, described for the first time by Y. Tabe and H. Yokoyama (Nat. Mater. 2003, 2, 806). Each of these two compounds have a polar group (which in Langmuir film is attached to water surface) and a chiral group at the opposite ends of the elongated molecules. The other two ferroelectrics have both groups at close proximity and therefore the chiral group is also attached to or even submerged in water. We demonstrate that the system is able to perform the collective molecular rotations only when the chiral group of the strongly polar liquid-crystalline molecule in the Langmuir monolayer is not attached to the interface and stays in the air strongly tilted. Because of a phase shift of rotation the stripe textures with rotating director can be created. The isotherms of surface pressure vs. molecular area of four compounds were measured with simultaneous observations with the aid of Brewster angle microscope.

Clip 1. The movie shows the collective rotation of molecules of compound C at 23°C on water surface. The images were taken with time delay 2 seconds and rotation is 5 times faster than in reality.

Figure 1. Examples of the textures of rotating phases most frequently observed in compounds B and C at the water/air interface. The images show the areas (2.08 × 1.00) mm2.

Figure 2. Schematic drawing of the molecular organization at the water/air interface for particular compounds in different phases.

Figure 3. Sequence of the images taken with time delay 2 s showing a frequency of molecular rotation in compound C; the areas denoted as 1 and 2 in image (a) rotate at different frequencies; white bar of length 200 μm on image (a) shows the scale.

P. Milczarczyk-Piwowarczyk, A. Żywociński, K. Noworyta, R. Hołyst, Collective Rotations of Ferroelectric Liquid Crystals at the Air/Water Interface Langmuir 2008, 24 (21), pp 12354–12363